Ceramic treating process

ABSTRACT

A new ceramic treatment process and product and, more particularly, a process for treating underfired porous partially vitrified relatively soft machinable refractory ceramic materials to produce hardened dimensionally stable end products at relatively low temperatures and the ceramic materials produced thereby which are suitable for application as bearings for undersea submergence, low temperature bearings for arctic vehicular and machinery applications, precision bearings for space use and liquid metal lubricated systems. The soft ceramics can be machined and shaped in the soft state and hardened by the process of this invention at temperatures well below normal vitrification temperatures with virtually no change in dimensions from the machined untreated ceramic to the treated and hardened end product. The present method comprises impregnating a ceramic oxide body with a solution of a chromium compound and heating the impregnated body to a temperature of at least 1,300*F which heating may precede or be preceded by impregnation and cure cycles of at least 600*F but less than the vitrification temperature of the ceramic oxide to harden the body.

' United States Patent 1191 Church -et a1.

[ ]*Mar. 25, 1975 1 1 CERAMIC TREATING PROCESS [75] Inventors: Peter K. Church; Oliver J. Knutson,

both of Colorado Springs, C010.

[73} Assignee: Kaman Sciences Corporation, Bloomfield, Conn.

211 Appl. No.: 362,332

Related US. Application Data [63] Continuation-in-part of Ser. No. 642,704, June 1, 1967. abandoned. 1

Primary Eramtuer-William D. Martin Assistant Examiner-Sadie L. Childs Attorney, Agent, or F irm-Edwards, Spangler, Wymore & Klaas [57] ABSTRACT A new ceramic treatment process and product and, more particularly, a process for treating underfired porous partially vitrified relatively soft machinable refractory ceramic materials to produce hardened dimensionally stable end products at relatively low temperatures and the ceramic materials produced thereby which are suitable for application as bearings for undersea subme'rgence, low temperature bearings for arctic vehicular and machinery applications, precision bearings for space use and liquid metal lubricated systerns. The soft ceramics can be machined and shaped in the soft state and hardened by the process of this invention at temperatures well below normal vitrification temperatures with virtually no change in dimensions from the machined untreated ceramic to the treated and hardened end product. The present method comprises impregnating a ceramic oxide body with a solution of a chromium compound and heating the impregnated body to a temperature of at least 1,3 0OF which heating may precede or be preceded by impregnation and cure cycles of at least 600F but less than the vitrification temperature of the ceramic oxide to harden the body.

1 22 Claims, N0 Drawings CERAMIC TREATING PROCESS This application is a continuation-in-part application of US. Letters Pat. Ser. No. 642,704 filed June 1, 1967 for Ceramic Treating Process and Product Produced Thereby, now abandoned in favor of Continuation application Ser. No. 063,998, filed June 18, 1970, issued as U.S. Pat. No. 3,734,767 on May 22, 1973.

The process of treating underfired porous partially vitrified relatively soft refractory ceramic according to Applicants patent comprises the steps of shaping an underfired partially vitrified relatively soft refractory ceramic into a predetermined shape, impregnating the shaped ceramic with a solution of a chromium compound and curing the impregnated ceramic at temperatures of at least 600F, but below vitrification temperatures for a time sufficient to convert the compound to the oxide and produce a hard ceramic.

Ceramic materials normally undergo substantial dimensional changes during the usual firing or vitrification steps. Thus, it has heretofore been extremely difficult to produce a precision parts or intricate shapes from ceramics. Precision parts had to be shaped slightly oversize before firing. After firing, the parts required further machining with diamond cutting wheels or by using lapping methods. Many intricate shapes were just not available since thin sections of parts would crack during firing.

in accordance with the present invention, it has been found in Applicants process that the curing of the chromium compound impregnated ceramic body with at least one cure cycle at a temperature of at least about l,300F to as high as about 2,300F and higher, but less than the vitrification temperature of the ce ramic body, which cure cycle may either precede or be preceded by impregnation and cure cycles at least 600F, but less than the vitrification temperature, to convert the impregnant to an oxide materially increases the hardness of the body. Thus, the underfired or socalled machinable grade refractory ceramics can be shaped while in the relatively soft state and then impregnated and heat treated to produce a ceramic having all the characteristics of a vitrified ceramic without the usual change in dimensions. The process of the instant invention appears to be useful in the treatment of such refractory ceramic materials as the oxides of aluminum, beryllium, zirconium, titanium, magnesium and the like. These materials in the commercially available machinable grade are quite soft and easily, broken. Also, in the soft state, they can be readily cut with carbide cutting tools, drilled, filed, sanded and otherwise formed to practically any desired shape. One such aluminum and beryllium oxide material is available from Coors Porcelain Company of Golden, Col, When the machinable ceramics are treated by the method of this invention, they become very hard, approximating highly vitrified ceramic and, in addition, will retain the original machined and pre-treated dimensions. The treated material becomes so hard that the only practical method to do further machining is with diamond cutting wheels or by using lapping techniques.

The commercial value of the instant is readily seen when it is recognized that close tolerances on many intricate vitrified ceramic ports can only be obtained by machining with diamond cutting methods after firing. This is the case since there is considerable shrinkage which occurs during the firing. Also, there are many desired shapes which cannot be economically cast or molded during the firing process. In addition, it is often not feasible to construct molding dies for small quantities of a particular part. The method of the present invention in contrast thereto permits easy machining of parts to exact tolerances and then hardening the part without change in original dimensions.

It is, therefore, the principal object of this invention to provide an improved process for shaping, treating and hardening of machinable ceramics which avoids one or more of the disadvantages of prior art methods of producing close tolerance hardened shaped ceramic parts.

A further object of the present invention is to provide an improved process of producing hardened ceramic articles of manufacture of predetermined shapes, of predetermined characteristics and of predetermined dimensions.

Another object is to provide an improved method of producing close tolerance ceramic shapes of selected hardness, porosity and surface characteristics.

A still further object of the invention is to provide an improved method of obtaining increased hardness over that obtained heretofore. For a better understanding of the present invention, together with other and further objects thereof, reference is bad to the following description, and its scope will be pointed out in the appended claims.

This invention is directed to a process and product involving a new type of ceramic material that is formed by chemically impregnating a relatively soft porous, underfired refractory oxide base material, followed by a low temperature cure. The resulting ceramic structure formed in this manner has been shown to exhibit extreme hardness, a high compressive strength and a dimensionally stable material over a wide temperature range. in addition, a number of these new ceramic materials show an inherently small coefficient of friction coupled with a very low wear rate characteristic.

Parts can be economically fabricated of this new ma terial in a wide variety of intricate shapes and sizes. This is most easily accomplished by machining the relatively soft and porous refractory oxide base material to the final dimensions desired using conventional high speed steel or carbide tooling. The machined pieces are then chemically treated and cured at a temperature substantially below that used for normal ceramic vitrification.

One of the unique features of this chemical treatment and hardening method is that virtually no change will occur in the original dimensions of the machined part during the hardening process. Therefore, expensive diamond machining of the finished hardened part is eliminated.

These new ceramic materials will withstand repeated water quenching from 1,000F. as well as prolonged exposure to temperature extremes of 2,000F. to 300F. Mohs scale hardness is in excess of 9, normally being about equal to that of silicon carbide. Rockwell hardness can be as high as A- to A-90, with associated compressive strengths in excess of 125,000 psi.

In addition to their use for the manufacture of precision parts, many of these ceramics exhibit excellent characteristics for low friction and low wear rate bearing and seal applications: in particular, journal bearings, thrust bearings and sliding type bearing and seals. When used in this manner, lubrication may be by means of a wide variety of conventional and nonconventional lubricants. Among those successfully tested to date include: tap water, sea water, alcohol, kerosene, polyethylene glycol trichloroethylene, lubrieating oils, silicone fluids and liquid metals. Solid lubricants have been used with good results at temperatures up to about 2,000F. In addition, lightly loaded bearings have been operated for limited periods at high speed without lubrication.

Life tests of sleeve-type bearings have been and still are currently in progress. However, to date wear has been too low to obtain quantitative data, even after many months time. Rub-shoe type wear rate tests have consequently been conducted and have shown exceptionally low wear rate characteristics. For example, a ceramic shoe of this invention riding on a ceramic wheel of the same material exhibited many times less wear than a bearing bronze shoe riding against a steel wheel using oil as the lubricating media. Also, unlike a conventional bronze-steel bearing combination, very heavy loads can be applied to many of the ceramic-toceramic material bearings without their showing any tendency toward galling, even when running with such poor lubricants as alcohol or water.

A special variation in treatment of this invention has also been found that will produce a honing or finishing material that appears to be superior in several respects to both natural and artificially produced grinding stones. For example, one such ceramic will remove metal for more rapidly than will on Arkansas stone, while at the same time producing a finer and more highly polished finish. Another ceramic material of this invention displays a wide variation in electrical and heat conduction with relatively small changes in temperature.

The basic method employed for producing the new ceramic materials consists of chemically impregnating a porous, refractory oxide structure followed by a low temperature cure. The porous refractory acts as the skeletal framework around which the final ceramic structure is formed.

TABLE l The simplest chemist hardening method consists of impregnating the porous refractory structure with a solution of phosphoric acid. The thoroughly impregnated material is then cured in an oven with the final temperature reaching at least 600-l000F. or higher. With a suitable refractory base material, this simple acid treatment will produce a hard ceramic body having numerous uses.

A more dense, harder and structurally stronger ceramic can be formed by impregnating the porous base material with one or more refractory oxides prior to the final acid treatment. This may be accomplished by impregnation of the porous structure with a water soluble metal salt solution and subsequently converting to the oxide by simply elevating the temperature to the required conversion point. Normally, this salt to oxide conversion will take place at a temperature less than about 1,000F.

X-ray diffraction tests indicate that these chemical treatment methods form a new microcrystaline structure or at least a very close bond between the added oxides, and/or phosphoric acid and the phorous refractory skeletal structure.

As mentioned previously, the ceramic material is built around a porous refractory base material that functions as the skeletal structure. The types of such materials that are suitable for use in the present invention include various grades of alumina, titania, beryllia magnesia, magnesium silicate and stabilized zirconia. Silica has been tested but does not provide satisifactory results. These materials were obtained from the manufacturer in an underfired or machinable form. In this condition, these materials were normally found to be soft enough to allow machining by conventional means, and exhibited a relatively high effective porosity (10% to to allow for subsequent chemical treatment by the process of this invention. Table I lists the major type designation, manufacturer, hardness, porosity and fabrication method for each of the skeletal refractory materials tested.

UNDERFIRED, POROUS REFRACTORY BASE MATERIALS Manufacturers Base Type Manu- Major Other Sintering Effective Muhs Material Designation facturer Oxide Oxides Temp. Porosity Hardness Remarks Alumina AHP-99 Coors 99% A|. .O;, O 5% SiO., 2670F 45.7% 2-3 lsostatic 0 2% Cad Pressed 0 2% Mg() Alumina AP-99L3 Coors 99% A|,0,, 2570F 4 .4% 2-3 Extruded Alumina AP-99l l Coors 99% A1 0 l700F O-l Extruded Alumina AP-99-l2 Coors 99% Ago, 2l30F l Extruded Alumina AP-99-Ll Coors 99% A1 0; 2642F Extruded Alumina AP-99-L2 Coors 99% AI. ,O; 2670F 5-6 Extruded Alumina AP-99C-Ll Coors 99% A1,.0, 2642F 4-5 Cast Alumina AP-99C-l2 Coors 99% M 0 2l30F Cast Alumina AP-99C-L3 Coors 99% AI. .O;, 2570F Cast Alumina AP-995-L3 Coors 99.5% Al O 2570F Extruded Alumina AP-997L3 Coors 99.7% Al O 2570F Cast Alumina AP-9-l-ll Coors 94% AI. .O,, 3.75% SiOn 33.1% 2-3 Extruded 0.9% CaO 0.75% MgO l700F 0.5% ZrO,

0.l% F0 0 Alumina AP-94-l2 Coors 94% Algofl 3 SiO 2130F 33.0% 2-3 Extruded 0.9% CaO 0.75% MgO 0.5% ZrO 0.1% F6203 Alumina Al-94l2 Coors 94% AI O do. 2130F 44.1% 2-3 lsostatic (lsostatic) Pressed Alumina Al a -ll ("ours M 0; l0% SiO l700F 33.4% 2-3 Extruded 2.75% MgO 0.75% BaO 0.25% Fc O,

TABL I pri twe v UNDERFIRED, POROUS REFRACTORY BASE MATERIALS Manufacturer's Base Type Manu- Major Other Sintering Effective Mohs Material Designation facturer Oxide Oxides Temp. Porosity Hardness Remarks Alumina AlSiMag 614 Am.Lava 9671 N 2000F 6-7 Too hard for (underfired) Corp. easy machining Alumina AlSiMag 614 Am.Lava 9671 A1 0 SiO 2000F l-2 ordered green,

(green) Corp. MgO fired for CaO 20 min at ZOOOF. 1 Extruded rod Alumina AlSiMag 393 Am.Lava 9071 Al O 4-5 Cor Alumina AlSiMag 548 ml Lava 99.8% Al O or Beryllia BP-96-l Coo is 9671 BcO 1700F l-2 Extruded Magnesia l87EA Du-Co 8971 MgO SiO 2000F l-2 Ceramics Magnesia l87E77 Du-Co 967: MgO SiO: 2000F l-2 Ceramics Magnesium AlSiMag 222 AnrLava MgO.SiO 2-3 Silicate Corp. Silica No. 3 Porosity Amersil, 9971 SiO 2-3 Hot Pressed lnc. Zirconia l72H20 Du-Co 95% ZrO 5% C110 1-2 Made from ZCA Ceramics Type F Coarse Grain Zirconia- (CaO stabilized) Titania AlSiMag I92 Am.Lava 98% TiO SiO 2()()OF 2-3 Ordered Green Corp. MgO fired min. Undcrfired) CaO at 2000F These materials are fabricated by one or more of several commercially used methods such as powder pressing, extrusion, isostatic forming or slip casting. The important factor, however, is that the formed or pressed oxide be only partially sintered since optimum sintering will result in a dense body with insufficient porosity to be usable in the chemical treatment method of this invention.

In addition to the alumina, beryllia, magnesia, titania and zirconia materials, it is anticipated that many of the other partially sintered refractory oxides would make applicable skeletal structures for the improved ceramic material. Among these would be the oxides of Barium, Calcium, Cerium, Chromium, Cobalt, Gallium, Hafnium, Lanthanum, Manganese, Nickel, Niobium, Tantalum, Thorium, Tin, Uranium, Vanadium, Yttrium and Zinc. Also, many of the complex-refractory oxides should be suitable base materials. Of the complexrefractories, only the magnesium silicate has been tested to date. Other complex-refractories that may be suitable if produced in a porous, partially sintered (underfired) form are Aluminum silicate, Aluminum titanatc, Barium-Aluminate, Barium silicate, Barium zirconate, Beryllium aluminate, Beryllium silicate, Beryllium titanate, Beryllium zirconate, CalciumChromite, Calcium phosphate, Calcium silicate, Calcium titanate, Calcium zirconate, Cobalt aluminate, Magnesium aluminate, Magnesium chromite, Magnesium ferrite, Magnesium lanthanate, Magnesium silicate, Magnesium titanate, Magnesium zirconate, Magnesium zirconium silicate, Nickel aluminate, Potassium aluminum silicate, Strontium aluminate, Strontium phosphate, Strontium zirconate, Thorium zirconate, Zinc aluminate, Z i r ic zirconiurnsilicate and Zirconium silicate.

The novel process according to the invention is particularly adapted to the treating of porous, partially vitrified refractory ceramics such as the oxides of aluminum, barium, beryllium, calcium, cerium, chromium, cobalt, gallium, hafnium, lanthanum, magnesium, manganese, nickel, niobium, tantalum, thorium, tin, titanium, uranium, vanadium, yttrium, zinc and zirconium and mixtures thereof. The oxides may be substantially pure or may contain or have small amounts of impurities or additives, such as an oxide of a metal other than that of the body such as copper, iron, chromium, manganese, nickel, titanium, magnesium, cobalt, cadmium and the like and/or other salts of such metals which ultimately will convert to oxides at least during the final curing step. The process of this invention also contemplates the addition of small amounts of additives such as a salt of a metal other than that of the body and convertible to an oxide such as the chlorides and nitrates of aluminum, copper, chromium, cobalt, magnesium, molybdenum, nickel, tin and zirconium which are added to the ceramic during treatment. it appears that the higher purity refractory ceramics are preferable where maximum hardness is desired.

The process of this invention comprises usually the forming of the untreated ceramic into a predetermined shape. lt will be understood that, while precast machinable stock may be used, it is possible to precase to intricate shapes and prefire to an underfired condition before the ceramic is subjected to Applicants process. The machinable ceramic, either stock or custom cast, is usually quite porous. The simplest method of chemically hardening the porous, underfired refractory structure is with a single acid treatment. The ceramic is impregnated with a concentrated phosphoric acid solution, usually of concentration. The ceramic can be evacuated in a vacuum before immersion in the acid to hasten the impregnation or, as has been found to be particularly effective, the ceramic can be heated to from about 300 to about 600F. and then immersed in the phosphoric acid solution. The heating causes a vacuum to be produced within the voids of the ceramic and the phosphoric acid will be drawn all through the ceramic upon immersion. While a considerably larger time is required, the ceramic also can be just immersed in the acid solution for a length of time sufficient for complete impregnation. Greater uniformity is achieved by using the vacuum or heating impregnation techniques. When the part is thoroughly impregnated with acid, it is removed from the solution, excess acid on the surface is drained or wiped off.

Next, Applicants novel process comprises the controlled heat curing of the acid impregnated ceramic. The heating cycle is usually started around 150F. and ends at about at least 900F. The ceramic pieces are preferably placed in powdered asbestos, and the like, to minimize shock during the heating and cooling cycle. The powdered asbestos also serves to absorb moisture driven out of the ceramic as the temperatures is raised. The temperature is raised during curing at a rate insufficient to craze the surface of the ceramic.

As pointed out, one of the unique features of the method of the invention is that virtually no dimensional changes occur in the machined pieces during the hardening process. Therefore, expensive diamond-type machining of a hardened part is eliminated.

The property of physical hardness has been used as the primary means of determining effects of varying the underfired base materials, chemical treatment and curing methods. Table II below sets forth the hardness measurements for various materials which have been given a simple acid treatment.

Where the ceramic material is impregnated with or higher concentration of phosphoric acid and heat treated, a good bearing material is produced and two pieces of this same material will slide against one another with a low coefficient of friction. After such pieces are worn in for a short while, a shiny surface film is produced which remains shin even at elevated ternperatures. Where the more concentrated phosphoric acid is used, the resulting product is more dense with smaller unfilled pores. Where a relatively pure ceramic oxide is treated, the addition thereto of another oxide during treatment substantially increases the hardness of the finished product. While it is not completely known what occurs in the treating process, the pores of the underfired ceramic are believed to be filled or partially filled with a reaction product of the ceramic and the additive, if any, with the acid, probably a complex metal phosphate.

Where the ceramic material is impregnated with 85% or higher concentration of phosphoric acid having dissolved therein aluminum phosphate crystals until saturated at from 250-400F. and is then heat treated, a material is produced which cannot be polished to more than a dull finish, is quite porous and makes an excellent polishing and sharpening stone. This characteristic is also produced where the treatment with phosphoric acid is carried out with dilute acid solutions. It is believe that less reaction product is available to fill the pores, providing a more open and abrasive surface. Here again, the addition of another oxide treatment substantially increases the hardness of the final product. The starting porous aluminum oxide grades have TABLE ll HARDNESS MEASUREMENTS FOR SIMPLE AClD TREATMENT Sample Base Type Major H;,PO Molis Rockwell No. Material Designation Manufacturer Oxide lmpregnation Hardness Hardness Remarks ZIE Alumina AP-8S-ll Coors 85% Al. ,O 85% 8-9 A-66.5

22E Alumina AP94-ll Coors 94% A1 0;, 85% 6-7 A-69.5

23E Alumina AP-94-l2 Coors 94% A1 0; 85% 6-7 A-7l.()

24E Alumina AP-94-l2 Coors 94% A1 0 85% 7 A-57.5

(isostatic) 25E Alumina AP-99-L3 Coors 99% A1 0 85% 8-) A-7().5

20E Alumina AHP-99 Coors 99% M 0; 85% 6-7 A-5l5 A7 Alumina AlSiMag 614 Am. Lava Corp. 96% AI O; 85% 8-9 A-73.7

(underfired) 30E Alumina AlSiM-ag 393 Am. Lava Corp. AI O 85% 8-9 fractured 29E Alumina AlSiMag 548 Am. Lava Corp. 99.8% Alf); 85% o-7 fractured 16E Beryllia BP-Ki-l l (ours 96% BcO 85% (F7 fractured a-l Magnesia l87E-l [)u-(o (er-antics 89% Mg() 85% 4- 5 Fractured 6 l Magnesia l87F.77 Du-Co ('cramics 96% Mg() 85% 4 5 A471) 28-h Magnesium AlSiMag 222 Am. Lava Corp. MgO.Si()- 85% Silicate 'l7-E Silica No.3 porosity Amcrsil, Inc. 99% SiC) 85% Fractured 5o-T Titania AlSiMag I92 Am. Lava Corp. Tio 85% 4-5 Fractured (underfired) Z-l Zirconia l7ZHZO Du-Co Ceramics 95% ZrO 85% 8-9 A-5-l.l)

44T Alumina AjlggMa Am. Lava Corp. MgO.SiO. 85% 5-6 A-o5.5

C60 Alumina AP-99C-l2 Coors 99% AL O 85% 146 Alumina AP-99C-Ll Coors 99% A1 0 85% A-o6.4

Several significant differences in the final product are 60 ranged from about 25% to about 60% effective porosity achieved by the variation of portions of the treating process. While a pure or nearly pure ceramic material can be significantly hardened by a simple acid treatment, impregnation of the ceramic with a solution of a salt convertible to an oxide and converting same to the oxide will produce an increase in the hardness of the ceramic and the further acid treatment produces on even harder end product.

and, when subjected to a starved acid treatment, re main quite porous which may account for the excellent polishing and sharpening characteristics of the thus treated material.

The heat treating of the acid impregnated ceramic should be initiated at about 150F. to 350 F. for a short period of time to drive out excess moisture and then the temperature is raised in steps for a series of time intervals until the final cure is accomplished at at least 500600F. and preferably at at least 850900F. The ceramic will become quite hard at 500F.600F., but good electrical resistivity is not achieved until the ceramic is subjected to a temperature of 850F. or higher. Temperatures above 1,000F. and as high as 3,000F. have been used with good success. It is found that, once the heat treatment has been carried to above 850F., the temperature may be increased to well above the normal vitrifying temperatures (e.g.,3,000F.) without producing any shrinkage or change in the original physical dimensions. Further, the high temperatures do not appear to affect the hardness of the material from that of the material heated to 850F.

While the mechanism of Applicantsprocess is not completely understood, it is belived that aluminum phosphate may be formed and deposited in the crystal lattice structure of the aluminum oxide as well as within the voids of the porous ceramic. Further, the phosphates of the inpurities and/or additives may be formed and possibly as part of the lattice structure.

As pointed out above, the ceramic materials which are chemically treated and hardened according to one embodiment of the present process display the unique characteristic of exhibiting a low coefficient of friction when sliding against themselves. The coefficient of fric tion between identical pieces of the material is consid erably less than when used incontact with any dissimilar ceramic or metal tested to date.

Although these materials may be operated dry where they are lightly loaded for limited periods of time, the starting friction is considerably higher than when a lubricating material is present. Lubrication may be by a number of different liquids such as tap water, sea water, kerosene, trichlorethylene, lubricating oils, silicone fluids and liquid metals. Dry lubricants such as molybdenum di-sulfide, graphite and the like are also suitable. [t is possible also to form the lubricant in situ within the pore structure of the bearing.

The bearings can be easily and economically fabricated in a wide variety of shapes and sizes. The untreated ceramic material in the form of partially fired bars or plates is machined to size and shape using conventional high speed steel or carbide tooling. The machined pieces are then chemically treated and hardened at temperatures substantially below normal vitrification temperatures. The hardening occurs with substantially no change in dimensions, thus avoiding expensive diamond machining of the finished part.

The ceramic bearing being fairly porous may be used as the lubricant reservoir analogous to that of sintered bronze bearings, In other instances, the bearing can be operated partially or totally submerged in the lubricant or the non-rotating member can be connected to an ex ternal lubricant reservoir.

Typical bearings fabricated of ceramic according to the present invention can withstand repeated water quenching from at least 1,000F., as well as prolonged exposure to temperatures as high as 2,()F. and as low as 300F. The compressive strength is on the order of about 125,000 psi or better, and the hardness on the Mohs scale is between 910 or on the order of about A'80 A-90 on the Rockwell scale.

The ceramic materials of Table l were subjected to several slightly different treatments according to this invention, which are: (l) impregnation in phosphoric acid alone; (2) one or more oxide impregnations fol- Ml lowed by a single phosphoric acid treatment; or, (3) one or more oxide impregnations alone.

A typical acid impregnation process according to the present invention comprises heating the ceramic piece to about 300 600F. for about 20 minutes, the piece is then immersed in an phosphoric acid solution while hot for about 40 minutes. The piece is then placed in an oven and progressively heated from 150F. about 1,000F. over a period of about minutes. The piece is then cooled to room temperature.

A typical combination salt and acid impregnation process comprises heating the ceramic piece to about 250 450F. for about 20 minutes. The heated piece is then immersed in the salt solution for about 40 minutes. The piece is removed from the salt solution and cured progressively from F. to l,0()OF. over a period of 120 minutes. The previous step can be repeated if desired. The piece is then cooled to about 600F. and immersed in an 85% phosphoric acid solution for about 40 minutes. The piece is then placed in an oven and cured over a temperature range of from 150F. to l,()00F. over a period of about 120 minutes and subsequently cooled to ambient temperature in about 15 minutes.

Fully hardened samples were prepared according to the above treatments from the materials of Table 1.

As previously stated, impurities existing in the base material appear to have an effect on the resultant hardness of the treated piece. Therefore, it was decided to artificially add refractory oxides to the porous base structure prior to treating with the acid. This was accomplished by impregnating the refractory base material with a nitrate, chloride, acetate or other highly water soluble salt of the oxide desired, and then converting the salt to the metal oxide by heating slowly to an elevated temperature. Following the oxide imprcgnation (which may consist of one or more salt treatments), the body was then treated with phosphoric acid in the same way as in the acid treatment alone.

Tables III, IV, V and Vl show the effect of added ox ides to Coors alumina products AHP-99, AP-99-L3, AP-94-ll and AP-85-l 1, respectively. In these tests, three impregnations of the saturated salt were used (to assure ample loading with the desired oxide), fol lowed by the 85% phosphoric acid treatment.

It is interesting to note that these tables show a wide variation in hardness depending on the oxide treatment. In some cases, the hardness is considerably increased over that of the same base material treated with acid only, while in others, the increase is not so marked. The hardness that is obtained with the acid treatment only (no oxide impregnation) is listed for comparison purposes.

The CF03 treatment is of special interest in that, when used with the 99%, 94% and 85% A1 0 base structures, the resulting ceramic is exceptionally high in hardness as compared to all other oxide impregnations tested. These four tables also show that the AHP- 99 material (99% A1 0 is the poorest choice for the base structure of these four types. However, since the AP-99L3 is also a 99% alumina composition, it must be assumed that the hardness is not a factor of the refractory purity alone, but that the other factors such as difference in effective pore size is probably resonsible for some or all of the noted differences.

Tables VII, VIII and IX show the same type of data using alumina oxides secured from the American Lava Corporation as their types 393, 548 and underfired 614. These are 90%, 99.8% and 96% A1 0 compositions, respectively.

Hardness measurements obtained with Coors 96% beryllium oxide for four different salt impregnations is shown in Table X. It is interesting that this base material produces results about equal to the best alumina material tested (Coors AP-99), indicating that refractory skeletal structures other than alumina are definite candidates for the ceramic fabrication method.

Tables XI and XII show hardness results for oxide impregnated magnesia material. While the hardness are quite low as compared to the alumina or the beryllia, this is to be expected since magnesia, even in its fully fired state is not a particularly hard material (Mohs 5-/2).

Tables XIII and XIV cover AlSiMag No. 222 mganesium silicate and Amersil 99% silica, respectively. For reasons not fully understood, refractory base materials containing a high percentage of silica do not appear to respond well to the chemical hardening method. Even in these two tests, however, the chromic oxide impregnation provided noticeably better results than the other impregnations used.

Table XV lists results obtained with a partially sintered, zirconia refractory base material. This particular underfired zirconia was fabricated from a calcia stabilized but coarse grain material. It is anticipated that a fine grained zirconia, and possibly a magnesium oxide stabilized type, would provide better results. Nevertheless, the zirconia also reacts to the chemical hardening method .in the same general manner as does the alumina, magnesia and beryllia, and, to a lesser extent, the magnesia silicate and silica materials. Table XVA lists results obtained with aluminum oxide material and Table XVB lists results obtained with titanium dioxide material.

With regard to the effect of pore size, it would be noted that the AHP-99 Coors material has quite large pores, compared to the other Coors material, being on the order of less than one micron compared with 2 to 3 mincrons for the AHP-99 materials. It would appear that the pore size would preferably be less than 2 microns and substantially uniform in size.

TABLE III HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USING COORS AP-94- I' ALUMINA REFRACTORY BASE MATERIAL (Acid Treated Hardness Mohs 8-9, Rockwell 707) Sample Oxide Salt No. Salt H;,PO. Mohs Rockwell No. Formed Impregnation Impreg. Imprcgnation Hardness Hardness Cracks Remarks 1 AI- O A|( N0 3 85% 9-10 A-7 1.5 None 7-l BeO BeCl- 3 85% 9-10 A-74.4 None 5 CaO Ca(NO 3 85% 8-9 A- 5 None 3 CdO Cd(NO 3 85% 8-9 A-63 None C-l CeO- Ce( N011): 3 85% 9-10 A-7 l .l None 9 C00 Co(NO 3 85% 8-9 A-7-l.8 None L-4 Cr O CrO 3 X 85% 9- I t) A-8 l .5 None 7-3 CuO Cu(NO 3 85% 9-10 A-6l.0 None 7 F820;; eCl 3 85% 8-9 A-72.5 None 7-5 La O LatNO h 3 85% 8-9 A-53.5 Yes 7-7 Li O LiC H o, 3 85% 8-9 A--l8.2 Yes I l MgO Mg(C H,O,). 3 85% 9-l() Fractured Yes D-5 MgCr O MgCrO, 3 85% 9- l A-73.8 None l3 l0 Ni(NO;,) 3 85% 9-l0 A-75.6 None D-l SnO SnCl 3X 85% 9- l A-7 l .7 None 15 SrO Srt NO;,) 3 85% 8-9 Fractured Yes 7-9 Th0: Th(NO;,) 3 85% 9-IU A-73.5 None l7 TiO Ti (C O 3 85% )-l() A-73.5 None a-x wo, H,siw,, 3 aw, 9-l0 A-72.l None Z1194 Zno ZnCl 3 85% 8-9 A-73.8 None D-3 ZrO ZrOCl: 3 85% 9- l A-7o.l None l-A Fe O;,.Crt ,O;, l )FcCl-,+ 3 85" 9-ll) A-77 None I l )CrO;

TABLE IV HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USING COORS AP-85-Il ALUMINA REFRACTORY BASE MATERIAL (Acid Treated Hardness Mohs 8-9, Rockwell /\-65.9)

Oxide Salt No. Salt H;,PO,, Molts Rockwell Sample No. Formed Impregnation Impreg. Impregnation Hardness Hardness Cracks Remarks 8-4 AI O,, Alt NO 3 85% 8-9 A-7l None 8-2 CeO Ce(NO;,). 3 85% 9-l0 A-7-1 Yes 8-] (r 0 (r0 3 85% 9-l0 A-l None 8-5 MgO Nlg(C- [H;!O2)2 3 85% 8-9 A-oo Yes Shattered During Rockwell Test 8-6 l l()2 THC- 0 3 85% 8-9 A-68 Yes Shattered During Rockwell Test 8-3 ZrO: 7.r()(l 3 85% 9-10 A-72 None TABLE V HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USING COORS AP-99-L3 ALUMINA REFRACTORY BASE MATERIAL (Acid Treated Hardness Mohs 8-9 Rockwell A-70l5) Oxide Salt No. Salt H -;PO Mohs Rockwell Sample No Formed lmpregnation Impreg. Impregnation Hardness Hardness Cracks Remarks L-4 CeO: Ce(NO;,) 3 85G 8-9 \-(\9.l Yes Exploded in Oven L-I CF00 CF03 3X 85F? 9-H) A-8(I.5 None L-3 MgCr O MgCrO; 3X 85' 9-l0 71,0 None L-2 ZrO- ZrOCI 3 85" 9-l0 \-60.1 None TABLE VI HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USING COORS AHP-99 ALUMINA REFRACTORY BASE MATERIAL (Acid Treated Hardness Mohs 5-6 Rockwell A-54.8)

Sample Oxide Salt No. Salt H PO Mohs Rockwell No. Formed Impregnation lmprcge Imprcgnation Hardness Hardness Cracks Remarks 2 AI 2O; AI(NO 3X 85% 8-9 A-60.0 None 7-2 BcO BcCI 3X 85% 8-9 A-5740 None 8-X BeO Be(NO;,) 3X 85% 6-7 A-67.9 None 6 Ca() Ca( N0 3X 85% 6-7 Fractured None 4 (d0 CLHNO I, 3X 85% 4-5 A-55.0 None (-5 (e0 Ce( N0 3X 85% 8-9 A-54.9 None l0 CoO (o( N07,), 3X 85% 6-7 A-62,2 None l\'7 (r 0 CrO 3X 85% 9- l 0 A-69.2 None 7-4 CuO CtHNO 3X 8571 4-5 A-47.l None 8 Fe O leCI 3X 85% 8-9 A-45.2 None 7-6 La O Lal NO 3X 85% 8-9 A59.0 None 744 l.i. ,O LiC H O 3X 85% 5-6 A-Sll Yes I: MgO M C- H,O.) 3x 85% (F7 A-Sl} Nom- K-3 MgCr O MgCrO 3X 85% 9 l0 A4335 None 14 Ni() Ni(NO 3X 85% 7-8 A-59.6 None 6-X IhO Ph(NO,) 3X 85% 5-6 A-55.l None -l-X Sb O, SbCl 3X 85?: 6-7 A-59.4 None D-Z SnO SnCI: 3X 85% 8-9 A-5l0 None lb SrO Sr( NO; 3X 85% 8-9 A-26.0 None 7-9 Th0 ThlNO l, 3X 85% 9-10 A-587 None l8 TiO. Ti. ,(C. Ia 3X 85% 8-9 A-53l3 None Ill-X WO H ,SiW 0 3X 859 8-9 A-69.0 None Zn-I ZnO Zn( NO,,) 3X 85% 8-9 A-48. I None A1199 [no ZnCI 3 85' 8-9 A-7l8 None I\'-5 [r0 7.r()(l 3 85% 8-9 A-6l.7 None TABLE VII HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USING ALSIMAG 614 (UNDERFIRED) ALUMINA REFRACTORY BASE MATERIAL* (Acid Treated Hardness Mohs 8-9. Rockwell A-73.7)

Sample Oxide Salt No. Salt H ,PO Mohs Rockwell No. Formed Impregnation lmpreg. Impregnation Hardness Hardness Cracks Remarks A4 1 0 Ce(NO;,). 3X 85% 8-9 A-69.0 None Fractured During Rockwell Test A-l4 Cr O- CrO;, 3 8571 9-10 A-76l0 None Al3 CoO Co(NO;,) 3X 85% 9-H) A73.0 None Fractured During Rockwell Test A-8 MgCr O MgCrO, 3 85 /1 9-H) A-65.5 None Fractured During Rockwell Test Al2 NiO Ni(NO; 3X 85% 6-7 A-7Z.5 None Fractured During Rockwell lest A-IO ZnO ZnlNO l 3X 85% 6-7 A-73.3 None A-9 ZrO- ZrOCl 3X 85% 9-10 A-68.0 None Fractured During Rockwell Tcst *Fired at Z000Fl TABLE VIII HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USING ALSIMAG 393 ALUMINA REFRACTORY BASE MATERIAL. (Acid Treated Hardness Mohs 8-9, Rockwell A-73l7) Sample Oxide Salt Noe Salt H POV Mohs Rockwell No. Forrncd Impregnation lmpreg. Impregnation Hardness Hardness (racks Remarks A-l CF30" (r0 3X 85'?) l 9-H) /\-77,() None A-5 MgCr O MgCrO 3X 85) I 9-l0 Shattered None A-6 /.r() ZrOCI- RX 859: P 8- 9 /\-68.5 None TABLE 1x HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USING ALSIMAG 548 ALUMINA REFRACTORY BASE MATERIAL (Acid Treated Hardness Mohs 6-7, Rockwell A-N Oxide Salt No. Salt H PO Mohs Rockwell Sample No Formed Impregnation lmpregl Imprcgnation Hardness Hardness Cracks Remarks A-l Cr- ,O CrO 3X 85% 8-9 Fractured None A-2 MgCr O MgCrO 3X 85% 8-9 Fractured None A-l ZrO: ZrOCI 3X 85% 8-9 A-76,4 None TABLE X HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNA'I'IONS USING COORS BP-96-ll BERYLLIA REFRACTORY BASE MATERIAL (Acid Treated Hardness Mohs 6-7. Rockwell A-N Oxide Salt No. Salt H PQ Mohl Rockwell Sample No. Formed Impregnation Impreg. Impregnation Hardness Hardness Cracks Remarks 8-] AI O; AI(NO;;)-; 3X 85% 8-9 A-74 None B-2 Cr O CrO; 3X 85% 9-10 A-Xl None Shattered in Rockwell Testing B-l MgCrO, MgCrO 3X X5% 9- l (I A-7 I None B-3 ZrO. ZrOCI 3X 85% 9-H) A-75 None Shattered in Rockwell Testing TABLE XI HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USING DU-CO 89% MAGNESIA REFRACTORY BASE MATERIAL (Acid Treated Hardness Mohs 4-5 Rockwell-Fractured) Oxide Salt No. Salt H;,PO., Mohs Rockwell Sample No. Formed Impregnation Impreg. Impregnation Hardness Hardness Cracks Remarks 9-! Al- ,O:, AI( NO 3X 85% 4-5 Fractured None 9-2 Cr O CrO;, 3X 85% 8-9 Fractured None 9-3 MgCr. ,O MgCrO. 3X 85% 8-9 A-5 1.5 None 9-6 IiO Ti (C O 3X 85% N.M. N.M. MgO Base Disintegrated 9-5 ZrO: ZrOU: 3X 85% N.M. N.M. MgO Base Disintegrated TABLE XII HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USING DU-CO 96% MAGNESIA REFRACTORY BASE MATERIAL (Acid Treated Hardness Mohs 4-5, Rockwell A-37.0l

Oxide Salt No Salt H;.P(),, Mohs Rockwell Sample No Formed Impregnation Impreg Impregnation Hardness Hardness Cracks Remarks 6-4 AI O; AI( NO 3X 85% 3-4 Fractured None 6-2 CrZ CrO 3X 85% 6-7 Fractured None o-l MgCr- -O MgCrO; 3X 85% 6-7 A-44.25 None 6-6 TiO Ti- .(C O 3X 85% N.M. N.M. Dissolved 6-5 Zr0 ZrOCI 3X 85% NM N.M. Dissolved TABLE XIII HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USING ALSIMAG Z22 MAGNESIUM-SILICATE REFRACTORY BASE MATERIAL (Acid Treated Hardness Mohs- 6-9, Rockwell A-N Oxide Salt No. Salt H PO Mohs Rockwell Sample No. Formed Impregnation Impreg. Impregnation Hardness Hardness Cracks Remarks MS-l AI O Al( NO 3X 85% 3-4 Fractured None MS- 2 Cr. .O;. CrO 3 X 85% 8-9 Fractured None MS-3 MgC O; MgCrO; 3X 85% 7-8 A-4I None Shattered During Rockwell Test MS-4 ZrO ZrOCl 3X 85% l-2 Fractured Nouc TABLE XIV HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USING AMERSIL No. 3 POROSITY SILICA REFRACTORY BASE MATERIAL (Acid Treated Hardness Mohs 4-5 Rockwell A-N Oxide Salt No. Salt H;,PO. Mohs Rockwell Sample No Formed Impregnation Impreg. Impregnation Hardness Hardness Cracks Remarks S-Z A1 Al( NO; 3X 85% 4-5 Fractured None S-6 (e0 Ce(NO 3X 85% 4-5 Fractured None S-l (r 0 CrO 3X 85% 6-7 A-54.() None S-3 MgO Mg(C H;,O 3X 85% 4-5 Fractured None S-5 MgCrO MgCrO 3 85% 6-7 Fractured None S-4 ZrO. ZrOCl 3X 85% 4-5 Fractured None TABLE XV HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USING DU-CO ZIRCONIA REFRACTORY BASE MATERIAL (Acid Treated Hardness Mohs 8-9, Rockwell A-54.0

Oxide Salt No. Salt H PO Mohs Rockwell Sample No. Formed lmpregnation Imprcg. Imprcgnation Hardness Hardness Cracks Remarks Z-4 AI. ,O Al(NO 3X 85% 6-7 A-46.8 None Z-Z Cr O; CrO;, 3X 85% 9-10 A-66.2 None Z-7 MgO Mg(C ,H O 3X 85% 6-7 Fractured None Z-3 MgCr O MgCrO 3X 85% 9-10 A-58.0 None 2-8 Tho Th( N0 3x ss /l (-7 A-55.3 None Z-6 ZnO Zn( N0 )2 3 s57, e 7 A-44.7 None Z-5 ZrO ZrOCl 3X 85% 8-9 A-60.3 None TABLE XVA HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USING ALSIMAG 614 96% A1 0 REFRACTORY BASE MATERIAL PARTIALLY SINTERED AT 2000F (Acid Treated Hardness Mohs 5-6. Rockwell A-N Oxide Salt No. Salt H PO Mohs Rockwell Sample No. Formed Impregnation Impreg. Impregnation Hardness Hardness Cracks Remarks T G 0 CrO 3X 85% 9-10 A-82.5 None 4IT ZrO ZrOCl 3X 85% 9-10 A-74.5 None 42T MgCr O MgCrO 3X 85% 9-10 Z-67.5 None 4ST NiO NIINOgI-g 3X 85% 9-10 A-69.5 None 44T None 85% 5-6 A-65.5 None TABLE XVB HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USING ALSIMAG I92 TITANIA 98% 110 REFRACTORY BASE MATERIAL PARTIALLY SINTERED AT 200F (Acid Treated Hardness Mohs 4-5 Rockwell A-N Oxide Salt No. Salt. H -,PO, Mohs Rockwell Sample No. Formed lmprcgnation Imprcg. Impregnation Hardness Hardness Cracks Remarks -T Cr O (r0 3X 85% 8-9 A-77.5 None 51-T ZrO ZrOCl- 3X 85% 8-9 A-66.0 None 52T BcO Be(NO-,)- 3X 85% 6-7 A-69.0 None 53T MgO Mg(C H,Os) 3X 85% 6-7 fractured 54T A1 0 Al( N0 3X 85% 5-6 fractured 5ST MgCnO MgCr O 3X 85% 9-10 A-65.0 56T one 85% 4-5 fractured Tables XVI-XXIX show the hardness of selected base materials which have been treated with multiple salt impregnations to illustrate the effect on hardness of varying the amount of added oxide prior to the final acid treatment. In the preceding Tables, all samples were impregnated with the salt solution three times. The following impregnations were varied from as few as one time to a maximum of eleven times. The base materials and oxide impregnations tested in this manner were selected from the materials of Table I.

Table XVI shows the effect of 1 through 11 chromie oxide impregnations using Coors AP-99-L3alumina base material, while Table XVIA shows the effect of 1 through 8 chromic impregnations with AP-94-1I alu- TABLE XVI HARDNESS VARIATION WITH NUMBER OF CHROMIC OXIDE IMPREGNATIONS USING COORS AP-99-L3 ALUMINA REFRACTORY BASE MATERIAL Oxide Salt No. Salt H -,PO Mohs Rockwell Sample No. Formed impregnation Impreg. impregnation Hardness Hardness Cracks Remarks 80-L c1 CrO IX 8571 9-10 A-73.2 None 81-L Cr O CrO 3X 8571 9-10 A-804 None 82-L Cr O CrO X 85% 9-10 A-83.9 None 83-L C O CrO 7X 85% 9-10 A-87.b

84-L Cr O CrO 9X 85% 9-10 A-88.3 None XS-L (r-:0 CrO 11X 85% 9-10 A-88.9 None TABLE XVIA HARDNESS VARIATION WITH NUMBER OF CHROMIC OXIDE IMPREGNATIONS USING COORS AP-94-I i ALUMINA REFRACTORY BASE MATERIAL Oxide Salt No. Salt H PO Mohs Rockwell Sample No. Formed impregnation Imprcg. impregnation Hardness Hardness Cracks Remarks L-X Cr O CrO 1X 85% 9-10 A-76.4 None L-9 (r- 0;, CrO 2X 8571 9-l0 A-80.7 None 3X (r 0 CrO 3 85% 9-10 A-81.8 None C r 0 C r0 4X 85% 9-10 5X CF" CrO 5X 85% 9-10 A-85.0 None 6X Cr- O CrO 6X 85% 9-10 A-85.0 None 7X Cr O; CrO 7X 85% 9-10 A-86.0 None 8X (r 0 CrO 8X 85% 9-10 A-8710 None obtained for a given number of treatments is much less than those obtained with chromic oxide treatment of Coors AP-99-L3 material of Table XVI. Since these alumina materials are both 99% aluminum oxide, and both have the same effective porosity of about the differences measured must be a result of the different pore size. The AHP-99 material has larger pores on the order of 2-3 microns average while the AP-99-L3 average pore size is 0.6-0.7 microns.

TABLE XVII HARDNESS VARIATION WITH NUMBER OF OXIDE IMPREGNATIONS USING COORS AP-94-l2 ALUMINA REFRACTORY BASE MATERIAL Oxide Salt No. Salt H PO Mohs Rockwell Sample No Formed impregnation impreg. impregnation Hardness Hardness Cracks Remarks 1,7 Cr O cro i 9-10 A-75.8. x-s Cr O c10 2 85% 9-10 A-79.6 L-4 Cr O cro 3x 85% 9 1 0 A-81.5 L-5 Cr O cro 4 85% 9-10 A-sss Z-S C 0 CrO 5X 8571 9-i0 A-8610 6X 8571 3-5 0 0 00. 7x 85% 9-10 A-83.0 4-s Cr 0 Cro 9x 85% 9-10 A-84.0 S-S Cr O CrO 11X 857! 9-10 A-85.()

TABLE XV HARDNESS VARIATION WITH NUMBER OF CHROMIC OXIDE IMPREGNATIONS USING COORS AHP-99 ALUMINA REFRACTORY BASE MATERIAL Oxide Salt No. Salt H -,PO., Mohs Rockwell Sample No. Formed impregnation imprcg. impregnation Hardness Hardness Cracks Remarks L-l (r 0 CrO;, 2X 85% 8-) A-ST-i None 1,: (lo no, 4x x was? None SU 0 0:, CrO;, 11 857: 9-l0 A-79.0

TABLE XIX HARDNESS VARIATIONS WITH NUMBER OF ZIRCONIUM OXIDE IMPREGNATIONS USING COORS AP-94-12 ALUMINA REFRACTORY BASE MATERIAL Oxide Salt No. Salt H PO Mohs Rockwell Sample No. Formed Impregnation Impreg. Impregnation Hardness Hardness C racks Remarks Y-l ZrO ZrOCI, IX 8571 8-9 A-71.9 None K-6 ZrO ZrOC1 2 85% 8-9 A-74.6 None 5-T ZrO ZrOCI 3 8571 9-10 A-70.() None 6-T ZrO ZrOCI 2X 85% 9-10 A-73.0 None 7-T ZrO- ZrOCI 5X 85% 9-10 A-73.0 None 8-T ZrO ZrOCI 8571 9-10 A-80.5 None 9-T ZI'Og ZrOCI 1 1X 85% 9-10 A-78.() None TABLE XX HARDNESS VARIATIONS WITH NUMBER OF ZIRCONIUM OXIDE IMPREGNATIONS USING COORS AHP-99 ALUMINA REFRACTORY BASE MATERIAL Oxide Salt No. Salt H;,PO Mohs Rockwell Sample No Formed Impregnation lmpreg. lmpregnation Hardness Hardness Cracks Remarks Y-Z ZrO ZrCI 1X 85% 5-6 A-55.5 None Y-4 ZrO ZrCl 2X 85% 9-10 A-63.5 None K-S ZrO ZrCI 3X 857r 9-10 A-6l.7 None Y- ZrO ZrCl 4X 85% 9-10 A-71i6 None verse is true when considering the AHP-99 material. Again, the explanation is undoubtedly connected with differences in pore size and/or impurities in the base 35 material.

Tables XXI and XXII show similar tests to those just chromate instead of zirconyl chloride.

TABLE XXI HARDNESS VARIATION WITH NUMBER OF MAGNESIUM CHROMITE IMIREGNATIONS USING COORS AP-94-12 ALUMINA REFRACTORY BASE MATERIAL described except that the impregnant was magnesium Oxide Salt No. Salt H PO Mohs Rockwell Sample No Formed lmpregnation lmpreg. lmpregnation Hardness Cracks Re-k mar 's M-l MgCr O MgCrO; 1X 85% 9-10 A-66 None M-Z MgCr O MgCrO 3X 8592 9-10 A-72 None M-i MgCr- O MgCrO 5X 8571 9-10 A-7O None TABLE XXII HARDNESS VARIATION WITH NUMBER OF MAGNESIUM CHROMITE IMPREGNATIONS USING COORS A HP-99 ALUMINA REFRACTORY BASE MATERIAL Oxide Salt No. Salt H PO Mohs Rockwell Sample No. Formed lmpregnation Impreg. lmpregnation Hardness Hardness Cracks Remarks M-4 MgCr O M gCrO 1X 85% 6-7 A-SO None M-S MgCr O MgCrO 3X 85% 9-10 A-53 None M-6 MgCr O M gC r0 5X 85% 9-10 A-61 None Tables XXIII and XXIV are for ceric oxide impregnated AP-94-ll and AHP-99 base material, respectively. Table XXV covers the AP-94 material with cobalt nitrate used as the impregnant. Table XXVI is for the same base material but using a concentrated silico- 5 cured.

TABLE XXIII HARDNESS VARIATIONS WITH NUMBER OF CERIC OXIDE IMPREGNATIONS USING COORS AP-94-Il ALUMINA REFRACTORY BASE MATERIAL Oxide Salt No. Salt H -,PO Mohs Rockwell Sample No. Formed Impregnation lmpreg. Impregnation Hardness Hardness Cracks Remarks C-O CeO- Ce(NOa)-2 2X 85% 8-9 A-68.3 None (-1 Ceo Ce(NO 3x 85% 9-10 A-7 1 ,l None C-2 Ce Cc(NO 4X 85% 9-]0 A-72.9 None C-J C00 Cc(NO 5 85V: 9-l0 A-74.6 None C-4 (e0 Ce(NO 6X 85% 9-K) A 75t7 None TABLE XXV HARDNESS VARIATION WITH NUMBER OF COBALT OXIDE IMPREGNATIONS USING COORS AP-94-l2 ALUMINA REFRACTORY BASE MATERIAL Oxide Salt No. Salt H,,PO Mohs Rockwell Sample No Formed Impregnation Impreg. Impregnation Hardness Hardness Cracks Remarks 3-B COO Co(NO; IX 8571 9-10 A-7I .5 None 2X 4-8 (oO Co(NO;,) 3 8571 9-H) A-73.t) None 4 I'T COO CHI NO);- 5X 9-IU A-7-I.5 Nuns TABLE XXVI HARDNESS VARIATION WITH NUMBER OF TUNGSTIC OXIDE IMPREGNATIONS USING COORS AP-94-I2 ALUMINA REFRACTORY BASE MATERIAL Oxide Salt No. Salt H;,PO Mohs Rockwell Sample No Formed Impregnation Impreg. Impregnation Hardness Hardness Cracks Remarks l-W W0, H SiW O IX 85% 8-9 A-690 None Z-W W0 H SiW O 3X 85% 7-8 A-7 l .0 None 5-W W0 H SiW O 4 8571 9- l 0 A-76.0 None 3-W W0 H SiW O 5X 85% 9-l0 A-76.0 None 3 4 I m 40 6X 85% 8-W W0 H SiW O 7X 85% 9-10 A-75.0 None TABLE XXVI] HARDNESS VARIATION WITH NUMBER OF FERRIC CHROMITE IMPREGNATIONS USING COORS AP-94-l2 ALUMINA REFRACTORY BASE MATERIAL Oxide Salt No. Salt H PQ Mohs Rockwell Sample No. Formed Impregnation Impreg. lmpregnation Hardness Hardness C racks Remarks 4-A Fe O Cr O l )Fe(l,, IX 8592 6-7 A-72 None (l)CrO,, 2X l-A Fe ();,(r,(); l )FegL, 3X 85% 9-H) A-75 None l )Cr Z-A Fe O Cr O=, l incl, 4 9-10 A-77 None l )CrO; 3-A Fc O Cr O l )FeCl: 5X 85% 9-10 A-SZ None I I n A zirconia base material has been used for tests shown as Tables XXVIII and XXIX. These are for a coarse grain, calcia stabilized, 95% zirconia underfired refractory material with chromic oxide and zirconium oxide impregnations as shown.

A series of multiple phosphoric acid treatments of the Coors AP-94, AHP-99 and AP-85 alumina base material has beeninvestigated. The results are shown TABLE XXVIII HARDNESS VARIATION WITH NUMBER OF CHROMIC OXIDE IMPREGNATIONS USING DU-CO. CALCIA STABILIZED, 95% ZIRCONIA BASE MATERIAL Oxide Salt No. Salt H;,PO Mohs Rockwell Sample No. Formed Impregnation lmpreg. Impregnation Hardness Hardness Cracks Remarks 20-Z C130 CrO 3X 85% 6-7 A-69.5 None 2 1-2 0 0;, 00;; 5X 85% 6-7 A-78.5 None 22-2 Cr- O CrO;, 7 85% 6-7 A-77 None 23-2 None None None 85% 8-9 A-54 None TABLE XXIX HARDNESS VARIATION WITH NUMBER OF ZIRCONIUM OXIDE IMPREGNATIONS USING DU-CO, CALCIA STABILIZED, 95% ZIRCONIA BASE MATERIAL Oxide Salt No. Salt n Po Mohs Rockwell Sample No. Formed Impregnation Impreg. Impregnation Hardness Hardness Cracks Remarks 23-Z ZrO ZrOCl 3 85% 6-7 A-65 None 24-Z ZrO- ZrOCl 5 85% 6-7 A-66 None 25-2 ZrO ZrOCl 7 85% 6-7 fractured 26-2 None None None 85% 8-9 A-54 None TABLE xxx MULTIPLE ACID IMPREGNATIONS USING COORS AP-94-l2 ALUMINA REFRACTORY BASE MATERIAL Salt No. Salt H PO No. Acid Mohs Rockwell Sample No. lmpregnation lnipreg. Impregnation Impreg. Hardness Hardness Cracks Remarks -l None 85% I X 8-9 A-o8.7 None P-Z None 85% 2X 8-) A-(17.8 None P-3 None 85% 3X 6-7 A-(i7.7 None P-4 None 42%71 I 4-5 A-6-l.8 Yes Fractured P-5 None 42147! 2X (i-7 A-58.7 Yes Fractured I-( None 43 /271 3X 0-7 A 58. None Fractured TABLE XXXI MULTIPLE ACID IMPREGNATIONS USING COORS AP-85-I I ALUMINA REFRACTORY BASE MATERIAL Salt No. Salt H PO No. Acid Mohs Rockwell Sample No. Impregnatlon lmpreg. lmpregnation Impreg. Hardness Hardness Cracks Remarks P-7 None 85% IX 8-9 A-6l.2 Yes P-8 None 85% 2X 9-l0 A-58.5 Yes Fractured P-9 None 85% 3X 6-7 A-63.() None P-IO None 42 /27: IX 4-5 A-53.7 None P-I I None 42 /29? 2X 6-7 Fractured Yes Fractured P-l 2 None 42 A /r 3 6-7 A-67.6 Yes TABLE XXXII MULTIPLE ACID IMPREGNATIONS USING COORS AHP-99 ALUMINA REFRACTORY BASE MATERIAL Salt No. Salt H PQ No. Acid Mohs Rockwell Sample No. Impregnation Impreg. Impregnation lmpreg. Hardness Hardness Cracks Remarks P-l3 None 85% P IX 5-6 A-44.2 None P-I4 None 85% P 2X 6-7 A-45.0 Yes Fractured P-l5 None 85% P 3 b-7 A-68.Il None l-R None 85% P 3X N.M. N.M. Yes 2-R None 85% P 4X N.M. N.M. Yes 3-R None 85%P 5 N.M. N.M. Yes 4-R None 85% I 6 N M. N.M. Yes P-l6 None 42-/fi% I IX 4-5 A-3 I .7 None 1. 7 None 42-'/1% P 2X 6-7 Fractured Yes Fractured P-l8 None 42-'/fi% P 3 6-7 A-4I.3 None TABLE XXXIII Salt No. Salt H;,PO No. Acid Mohs Rockwell Sample No. Impregnation Impreg. Impregnation Impreg. Hardness Hardness (racks Renun'ks I-C CrO 3X 85% IX 9-10 A-82.5 None 'J-C CrO 3X 85% 2X 9-10 A-XH) None 3-C CrO 3X 42// IX 9-l0 A-78.l None 4-C CrO 3X 42Vz'/1 2X Q-ll) A-XLI) None 5-C CrO 3X 42%9? 3X 9-II) A-XLI) None Tables XXXIV and XXXV show the effect of varying the phosphoric acid concentration. It the previous tests, the acid strength has been either 85% or 42- /2% H PO In these two tests 95%, 90% and 75% phosphoric acid are also compared with the standard 85% strength treatment. Table XXXIV covers the AP-94 base material and Table XXXV the AHP-99 material.

used as impregnants for one or more of the porous alumina base materials. A fifth impregnant, silico-tungsten acid, has also been found to react in a similar manner.

Tables XXXVI and XXXVII respectively show the hardness measurements obtained with AP-94-Il and AHP-99 alumina base materials with multiple chromic oxide impregnations only (no final acid treatment).

TABLE XXXIV EFFECT ON HARDNESS OF VARYING ACID CONCENTRATION USING COORS AP-94-l2 ALUMINA REFRACTORY BASE MATERIAL Salt No. Salt H PO No. Acid Mohs Rockwell Sample No. Impregnation Impreg. Impregnation lnipreg. Hardness Hardness Cracks Remarks 2 l-E None 95% [X 5-6 A-63.I) None 23-E None 85% IX 6-7 A-65.(l None 25-E None IX 6-7 A-59.5 None P- None 42 /271 l 4-5 A-64r8 None 27-E CrO 3X 95% IX 9-l0 A-83.I) None 29-E CrO 3X IX 9-10 A-80.5 None 3I-E CrO 3X 75% IX 89 A-82.0 None 3-C CrO 3X 42 /271 IX 9-10 A-8 I .0 None L-4 CrO 3X 85% IX 9-I0 A-8I.5 None TABLE XXXV EFFECT ON HARDNESS OF VARYING ACID CONCENTRATION USING COORS AHP-99 ALUMINA REFRACTORY BASE MATERIAL Salt No. Salt H;,PO No. Acid Mohs Rockwell Sample No. Impregnation Impreg. Impregnation Impreg. Hardness Hardness Cracks Remarks ZO-E None IX 4-5 A-46.() None 2 Z-E None 85% l X 6-7 A-56.0 None 24-E None 75% IX 6-7 A-46.() None P- I (v None 42%: [X 4-5 A 3 l.7 None lo-E (.rO 3X 95' IX 54 A-7Ill) None 28+ (rO 3 X $5) I X 4-5 A-7-l.() None 10+: 00.. 3x 752; I +5 A7l.5 None Table XXXVIII covers the same two base refractory materials with multiple magnesium chromite impregnations only and Table XXXIX shows the same Coors AP-9441 alumina material, but using multiple ferric chromite impregnations. Table XXXIXA shows the Coors AP-94-I2 material with multiple tungstic oxide oxides; magnesium chromite and iron chromite, when 55 impregnations.

TABLE XXXVI HARDNESS MEASUREMENTS FOR MULTIPLE Cr Q IMPREGNATIONS WITHOUT FINAL ACID TREATMENT USING COORS AP'94-l2 ALUMINA REFRACTORY BASE MATERIAL Sample Base Salt No. Salt H;.PO Mohs Rockwell I. Material Impregnation lmpreg. Impregnation Hardness Hardness Cracks Remarks O-I AP-94- I 2 CrO l None 4-5 A431) None 0-2 AP-94- l 2 CrO 2X None 4-5 A-62.2 None 0-3 AP-94- l 2 CrO 3X None 8-9 A-74.() None 0-4 AP-94- l 2 CrO;, 4X None 9-l0 A-82.0 None 0-5 AP-94-l2 CrO;, 5X None 9-l0 A-84.0 None 3'5 AP-94- I Z CrO;, 7 None 9-l0 A-84.U None -I-S AP-M- l 2 G0,, 9X None 9-l() A-84.5 None 5S AP-H- I2 CrO;, I l None 9-10 A'86.0 None TABLE XXXVII HARDNESS MEASUREMENTS FOR MULTIPLE Cr- ,O:, IMPREGNATIONS WITHOUT FINAL ACID TREATMENT USING COORS AHP-99 ALUMINA REFRACTORY BASE MATERIAL Sample Base Salt No. Salt H -,PO Mohs Rockwell r Material impregnation lmpregr Impregnation Hardness Hardness Cracks Remarks 0-6 AH P-99 C r0 IX None 3-4 A- l 5.2 None O-7 AHP-99 CrO 3X None 6-7 A-54v7 None 0-8 AHP-99 CrO 5X None 8-9 A-69.0 None 3-U AHP-99 CrO 7 None 9-10 A-75.0 None 4-U AHP-99 CrO 9X None 9-10 A-78.0 None 5-U AHP-99 CrO;, 1 I None 9-l0 A-79.5 None TABLE XXXVIII HARDNESS MEASUREMENTS FOR MULTIPLE MAGNESIUM CHROMITE IMPREGNATIONS WITHOUT FINAL ACID TREATMENT Sample Base Salt No. Salt H PO Mohs Rockwell No. Material lmpregnation lmpreg. lmpregnation Hardness Hardness Cracks Remarks M-l AP-94- I 2 MgCrO IX None 4-5 A-24.7 None M-Z AP-94- I 2 MgCrO 3X None 8-9 A491 None M-3 AP-94- I 2 MgCrO 5X None 9-H) A-63.l None M-4 AHP-99 MgCrO l X None 3-4 A-8.7 None M-5 AHP-99 MgCrO 3X None 6-7 A-28.8 None M-(w AHP-99 MgCrO 5X None 8-) A-39.() None TABLE XXXIX HARDNESS MEASUREMENTS FOR MULTIPLE IMPREGNATIONS WITHOUT FINAL ACID TREATMENT USING COORS AP-94ll ALUMINA REFRACTORY BASE MATERIAL Sample Oxide Salt No. Salt H;,PO., Mohs Rockwell No. Formed Impregnation Impreg. lmpregnation Hardness Hardness Cracks Remarks 4-A P6 0 0 0 1 )FeCl 1x 85% 4-5 1 r0; 5-A rc o c o I )FeCll. 3 85% 9-10 l a o-A Fto cr o- 1 )Ft-Ct, 5x 85% 9-10 l l zt TABLE XXXIXA HARDNESS MEASUREMENTS FOR MULTIPLE TUNGSTIC OXIDE IMPREGNATIONS WITHOUT FINAL ACID TREATMENT USING COORS AP-94-l2 ALUMINA REFRACTORY BASE MATERIAL Sample Base Salt No. Salt H PO Mohs Rockwell No. Material impregnation Impreg. Impregnation Hardness Hardness Cracks Remarks l-W AP-94- l 2 H SiW 0 l X None 4-5 A-35.0 None 3X None 7-8 fractured None 4X None 8-9 A-75rO None 5X None 8-9 A-69.5 None 7-W 6X None 9-IO A-65.0 None 7 None 9-l0 A-74.0 None Compressive strength tests have been conducted for several treated refractory ceramics using the ASTM tentative standard, Method C528-637.

TABLE XL COMPRESSIVE STRENGTH MEASUREMENTS FOR COORS AP-94-ll ALUMINA REFRACTORY BASE MATERIAL USING SINGLE ACID TREATMENT ONLY Sainp Salt No. Salt H -,PO Sample Area Compressive No. impregnation lmpreg. impregnation Diameter (in'-') lbl- Strength Remarks 1 None 8571 .622 .303 22.7K 74x11!) psi 2 None 8571 .623 .304 232K 76.500 psi TABLE XL Continued COMPRESSIVE STRENGTH MEASUREMENTS FOR COORS AP-94-I I ALUMINA REFRACTORY BASE MATERIAL USING SINGLE ACID TREATMENT ONLY Sample Salt No. Salt H PO. Sample Area Compressive No. impregnation Impreg. impregnation Diameter (in' lhf Strength Remarks 3 None 8571 .625 .306 24.2K 82.200 psi 4 None 8571 .622 .303 16.2K 53.500 psi 5 None 85 1 .622 .303 224K 74.000 psi 72.500 psi TABLE XLI COMPRESSIVE STRENGTH MEASUREMENT FOR COORS AP-94-I2 ALUMINA REFRACTORY BASE MATERIAL USING SINGLE ACID TREATMENT ONLY Sample Salt No. Salt H PO Sample Area Compressive No. impregnation Impreg. impregnation Diameter (in-') lbf Strength Remarks I None 85% .622 .303 263K 87.000 psi 2 None 85% .623 .304 2I.8K 71,800 psi 3 None 85% .625 .306 257K 83,800 psi 4 None 85% .621 .302 290K 94.000 psi 4 None 85% .624 .305 22.0K 72.300 psi Avg 8 I .800 psi TABLE XLII COMPRESSIVE STRENGTH MEASUREMENTS FOR COORS AP'85-I I ALUMINA REFRACTORY BASE MATERIAL USING SINGLE ACID TREATMENT ONLY Samp Salt No. Salt H -,PO Sample Area Compressive No. impregnation Impreg. impregnation Diameter (in lhf Strength Remarks I None 8571 .625 .306 I7.8K 58.300 psi 2 None 8571 .625 .306 20.0K 65.500 psi 3 None 8571 .625 .306 I2.6K 4 I .000 psi 4 None 8571 .624 .305 [2.7K 41,600 psi 5 None 8571 .623 .304 l8.95K 62.300 psi Avg 53.740 psi TABLE XLIII COMPRESSIVE STRENGTH MEASUREMENTS FOR COORS AP-99-L3 ALUMINA REFRACTORY BASE MATERIAL USING SINGLE ACID TREATMENT ONLY Sample Salt No. Salt H -,PO Sample Area Compressive No. impregnation Impreg. impregnation Diameter (in lbf Strength Remarks I None 8571 .625 .306 23.6K 77.400 psi 2 None 857: .624 .305 2 I .7K 7 I .000 psi 3 None 8571 .625 .305 2 I .6K 70.900 psi Avg 7.3.[00 psi 55 Tables XLIV, XLV and XLVI cover Coors AHP-99 base material with three impregnations of ehromie 0xide, magnesium chromite and zirconium oxide, respectively. A final, single acid treatment was also used in each case.

TABLE XLIV COMPRESSIVE STRENGTH MEASUREMENTS FOR COORS AHP-99 ALUMINA REFRACTORY BASE MATERIAL USING CHROMIC OXIDE IMPREGNATIONS PLUS SINGLE ACID TREATMENT Sample Salt No. Salt H;,PO Sample Area Compressive No. impregnation Impreg. impregnation Diameter (in) ihi Strength Remarks N-7 ('rO 3X R571 .149 .04) 3900 7lI.l00 psi N-J (r0 3X 8554 .250 .040 4475 30.600 psi ("-2 CrO 3X 85' .250 .04) 3750 76.375 psi (-3 (r0 3X 85' .250 .049 3050 62,3 70 psi TABLE XLIV Continued COMPRESSIVE STRENGTH MEASUREMENTS FOR COORS AHP-99 ALUMINA REFRACTORY BASE MATERIAL USING CHROMIC OXIDE IMPREGNATIONS PLUS SINGLE ACID TREATMENT Sample Salt No. Salt H -,PO Sample Area Compressive No. lmpregnation Impreg. Impregnation Diameter (in'-') lbf Strength Remarks C-4 CrO 3X 85% .249 .049 4375 89,835 psi Avg 80,249 psi TABLE XLV COMPRESSIVE STRENGTH MEASUREMENTS FOR COORS AHP-99 ALUMINA REFRACTORY BASE MATERIAL USING MAGNESIUM CHROMITE IMPREGNATIONS PLUS SINGLE ACID TREATMENT Salt No. Salt H PO Sample Area Compressive Sample No impregnation lmpreg. lmpregnation Diameter (m lbf Strength Remarks N-2 MgCrO 3X 85% .250 .0492 4175 83,600 psi N-3 MgCrO 3X 85% .250 .0492 3575 71,500 psi Avg 77,550 psi TABLE XLVI COMPRESSIVE STRENGTH MEASUREMENTS FOR COORS AHP-99 ALUMINA REFRACTORY BASE MATERIAL USING ZIRCONIUM OXIDE IMPREGNATIONS PLUS SINGLE ACID TREATMENT Salt No. Salt H PO Sample Area Compressive Sample No. Impregnation Impreg. Impregnation Diameter (in lbf Strength Remarks N-5 ZrOCl 3 8571 .249 .049 2375 47.500 psi N-o ZrOCI 3X 85% .250 .049 I800 86.050 psi Avg 41.775 psi Table XLVII shows compressive strength measurements for Coors AP-94-l 1 material with three chromie oxide impregnations, plus final acid treatment.

TABLE XLVII COMPRESSIVE STRENGTH MEASUREMENTS FOR COORS AP-94-ll ALUMINA REFRACTORY BASE MATERIAL USING CHROMIC OXIDE IMPREGNATIONS Salt No. Salt H;,PO Sample Area Compressive Sample No. impregnation Impreg. impregnation Diameter (in) lbf Strength Remarks (-5 CrQ', 3X 857: .25l .04] 6I00 123,730 psi C-6 CrO; 3X 8571 .Zfil i049 6600 I33,333 psi Avg 128,532 psi of the Coors AP-94-l2 base material with multiple (zero, three and six) chromic oxide impregnations and Table XLVIIIA lists the modulus of rupture tests for the Coors AP-99-L3 base material with multiple (three and six) chromic oxide impregnations and with chromic acid plus other oxide impregnations.

TABLE XLVIII MODULUS OF RUPTURE TEST DATA FOR COORS AP-94-l2 (ISOSTATIC) ALUMINA REFRACTORY BASE MATERIAL Salt No. Salt H PO Support Modulus Sample No. Impregnations lmpreg. impregnation Diameter Distance lbt ot Rupture Remarks I-R None 0.295 6% W100 Z-R None 8571 0.295 (18 10200 3-R (r0 3X 85% 0.293 92 |4,000 4-R Cr();, 3X 85% 0.292 ()5 10.000 'i-R CrO 6X 85'7/ 0.154 76 11.480

TABLE XLVIIIA MODULUS OF RUPTURE TEST DATA FOR COORS AP-99-L3 ALUMINA REFRACTORY BASE MATERIAL Salt No. Salt H PO Support Modulus Sample No. Impregnations Impreg. Impregnation Diameter Distance lbf of Rupture Remarks 7 None 85% .260 1.50 In. 82 17.900 9 CrO 3X 85% .258 125 27.900 10 3 857! .258 1 10 24,500 11 (1'0 6X 85% .258 84 18,700 12 6X 85% .260 W 164 35,700 13 4 ZrOU 2X 85% .258 71 148 33,000 14 n 4 2X 85% .257 1, 128 28.900 15 CrO 4 N13 10 2 85% .260 n 110 24,000 16 4 2 85% .258 124 27,600 17 CrO 4 H SiW O 2 .258 7 23,400 19 CrO 4 Be(NOn)2 2X 85% .258 80 17,800

Specific gravity determinations for a number of the To determine the effective porosity of these ceramic porous refractory base materials, measured in the rematerials, water absorption tests were made. The poitelsees iiqeleeereeatet n Tab eikylx txp r ema ewas 9 1 31 3 by determining the TABLE XLVIX SPECIFIC GRAVITY DETERMINATION FOR VARIOUS REFRACTORY BASE MATERIALS WITHOUT OXIDE OR ACID TREATMENTS (AS RECEIVED CONDITION) Base Salt No. Salt H PO, Volume Wt. in Air Length Diameter Specific Sample No. Material lmpreg. Impreg. Impreg. (cc) (Dry)(gn1s)(em) (em) Gravity A99 AHP-99 None Nonc 1.684 3.53 1.471 1.210 2.10 B93 AP-99-L3 None None 1.674 3.95 1.474 1.205 2.36 C51 AP-SS-ll None None 1.645 3.94 1.456 1.200 2.39 D41 AP-94-11 None None 1.678 4.15 1.478 1.205 2.47 E42 AP-94- l 2 None None 1.696 4.21 1.494 1.205 2.48 E421 AP-94-12 None None 1.678 3.60 1.478 1.204 2.14

(Isostatic) Specific gravity measurements for some of these weight of the absorbed water in grams dividedby the same materials, but processed with a single phosvolume of the sample in cub1c centimeters. Th1s type phoric acid treatment, is listed in Table L. of measurementg ives the effective poros1ty only smce TABLE L SPECIFIC GRAVITY DETERMINATION FOR VARIOUS REFRACTORY BASE MATERIALS WITH SINGLE ACID TREATMENT ONLY Base Salt No. Salt HHPO4 Volume Wt. in Air Length Diameter S ecifie Sample No. Material lmpreg. lmpreg. lmpreg. (cc) (Dry)(gms) (cm) (em) ravity A99 AHP-99 Ntmc 85% 1.71 4.31 1.494 1.210 2.52 A93 AP-99-L3 None 85% 1.678 4.63 1.474 1.206 2.75 A51 AP-85-ll None 7. 1.632 4.49 1.466 1.194 2.75 A41 AP-94-ll None 85% 1.671 4.74 A 1.475 1.2114 2.83 A42 AP-94-l2 None 14577 1.692 4.83 1.494 1.2114 2.85 A421 AP-94-12 NUIIL 859, 1.675 4.32 1.478 1.203 2.514

(Isostatic) Table Ll Shows Specific vity measurements for there may be completely entrapped pores or pores too Coors AP-99-L3 alumina base material with I through 55 small to admit water. 11 chromic oxide impregnations. This Table shows Table LII shows the effective porosity measurements that a maximum density was obtained with six made for a number of the porous, underfired refractory chr mi l p gnations. base materials prior to any treatment of any kind.

TABLE LI SPECIFIC GRAVITY DETERMINATIONS FOR COORS AP-99-L3 ALUMINA REFRACTORY BASE MATERIAL WITH MULTIPLE CHROMIC OXIDE IMPREGNATIONS Base Sall No. S1111 H PO Volume Wt. in Air Length Diameter Specific Sample No. Material lmpreg. Impreg. Impreg. (cc) ll rynglnsltcml (em) (:ravily 1 Alum (11) Nutty 1 117 1711 7111 1 3-14 .9 7/ I Al l lfl (41),. H5; I 9 1.2. .710 l 5. 5 1.09 .1 Al-99-l.1 C10 5* 115% 1.168 4.74 .714 1.56.1 3.46 4 AP-99-L] (r0 7x 14591 1.337 4.95 .704 1.555 3.70 5 AP-99 Li (r0 9X 85'71 1.391 .30 .726 1.563 3.8] 6 AP-99-L3 Cr();, 1 1X 85% 1.334 .07 .696 1.564 3.80

These materials show porosity variations ranging from about 30% to about 50% for the types tested.

TABLE LII perature excursion. The samples were left immersed until gas formation ceased and it is estimated that a Base Salt H PO Wt. Soaked Wt. in Air H. .O(gms) Volume Effective Sample No. Material Impreg. No. Impreg. in H O(gms) (Dry)(gms) Absorbed (cc) Porosity A99 AHP 99 None None 4.30 3.53 .77 1.684 45.7% B93 AP-99-L3 None None 4.66 3.95 .71 1.673 42.4% C51 AP-85-11 None None 4.49 3.94 .55 1.645 33.4% D41 AP-94-l1 None None 4.71 4. I .56 1.678 33.5% E42 AP-94-12 None None 4.77 4.21 .56 1.696 33.0% E421 AP-94-12 None None 4.34 3.60 .74 1.678 44.1%

(IsostatiC) temperature of about -300 F. had been reached. Again, no cracks or fatiguing were noticed after ten cycles.

I'ABLE LIII EFFECTIVE POROSITY DETERMINATIONS FOR VARIOUS REFRACTORY BASE MATERIALS WITH SINGLE ACID TREATMENT ONLY Base Salt H 1 0, Wt. Soaked Wt. in Air H O (gms) Volume Effective Sample No Material Impreg. No. Impreg. in H O(gms) (Dry)(gnis) Absorbed (cc) Porosity 99 AHP-99 None 85% 4.64 4.31 .33 1.710 19.3%. 93 AP-99-L3 None 85% 4.87 4.62 .25 1.678 14.9%. 51 AP-85-l1 None 85% 4.70 4.49 .21 1.632 12.9% 4.1 AP-94-11 None 85% 4.95 4.74 .26 1.671 12.6% 42 AP-94-12 None 85% 5.03 4.83 .20 1.692 11.8% 421 AP-94-12 None 85% 4.66 4.32 .28 1.675 16.7%

(isostatic) Table LIV presents data obtained by using 1 through 1 1 chromic oxide impregnations followed by the single acid treatment. In this test, Coors AP-99-L3 base material was used. As in the ease of the specific gravity These two thermal shock cyclings (1,000 F and liquid nitrogen) were repeated using AP-94-11 alumina base material. These samples were prepared, however, with three, five and seven chromic oxide impregnations measurements. minimum porosity occurs at about 9-11 prior to the final phosphoric acid treatment. In this impregnations. case, the samples measured approximately Vs inch in TABLE LIV EFFECTIVE POROSITY DETERMINATIONS FOR COORS AP-99L3 ALUMINA REFRACTORY BASE MATERIAL WITH MULTIPLE CHROMIC OXIDE IMPREGNATIONS Base Salt H;,PO Wt. Soaked Wt. in Air H O(gms) Vol- Effective UITIC Sample No. Material Impreg. No. Impreg. in H O(gms) (Dry)(gms) Absorbed (cc) Porosity 1 AP-99-L3 CrO l None 3.95 3.70 .25 1.337 18.2% 2 AP-99-L3 CrO: 3 None 4.52 4.23 .29 1.349 21.5% 3 AP-99-L3 CrO 5X None 4.95 4.78 .21 1.368 15.3% 4 AP-99-L3 CrO 7X None 5.10 4.95 .15 1.337 11.2% 5 AP-99-L3 CrO 9X None 5.32 5.30 .02 1.391 1.43% 6 AP-99-L3 CrO 11X None 5.08 5.07 .01 1.334 0.74%

Samples of AI-IP-99 alumina, with single acid treatment only, have been fabricated in the form of thin discs measuring A inch X 3 inches. They were then heated to 1,000 F. and water quenched, reheated to l,000 F. and again quenched for a total of ten cycles. No visible signs of cracking or checking were observed.

The same type test has been performed with similarly prepared samples using liquid nitrogen as the quenching media. While liquid nitrogen does not produce as severe a thermal shock as does a good conductor such as water, it does, however, provide a much wider tem- 

1. THE METHOD OF PRODUCING A CHEMICALLY HARDENED REFRACTORY CERAMIC BODY WHICH COMPRISES PROVIDING A CORE OF A POROUS UNDERFIRED PARTIALLY VITRIFIED MACHINABLE REFRACTORY CERAMIC OXIDE, IMPREGNATING SAID CORE WITH A SOLUTION OF A CHROMIUM COMPOUND WHICH COMPOUND IS CAPABLE OF BEING CONVERTED TO AN OXIDE ON BEING HEATED TO A TEMPERATURE OF AT LEAST 600*F AND, CURING SAID IMPREGNATED CORE AT LEAST ONCE BY RAISING THE TEMPERATURE THEREOF TO AT LEAST 600*F BUT LESS THAN THE VITRIFICATION TEMPERATURE OF THE CERAMIC OXIDE OVER A PERIOD OF TIME SUFFICIENT TO CONVERT THE CHROMIUM COMPOUND IMPREGNATED THEREIN TO AN OXIDE TO HARDEN THE CERAMIC WHEREIN AT LEAST ONE CURE CYCLE IS CARRIED OUT AT A TEMPERATURE OF AT LEAST 1,300*F BUT LESS THAN THE VITRIFICATION TEMPERATURE OF THE CERAMIC BODY.
 2. The method of claim 1 wherein there are at least two impregnation and cure cycles and all of the cure cycles are carried out at a temperature of at least 1,300*F.
 3. The method of claim 1 wherein there are at least two impregnation and cure cycles including one or more high temperature cure cycles of at least 1,300*F and one or more low temperature cycles of at least 600*F but less than 1,300*F.
 4. The method of claim 1 wherein the oxide body is aluminum oxide.
 5. The method of claim 1 wherein the solution is chromic acid.
 6. The method of claim 3 wherein the initial cure cycle is a high temperature cycle.
 7. The method of claim 3 wherein the initial cure cycle is a low temperature cycle.
 8. The method of claim 7 wherein the first five cure cycles are low temperature cycles.
 9. The method of claim 7 wherein the first ten cure cycles are low temperature cycles.
 10. The method of claim 6 where the cure cycles are alternately high and low temperature cycles.
 11. The method of claim 7 where the cure cycles are alternately high and low temperature cycles.
 12. In a process for hardening and densifying a ceramic body which includes the steps of impregnating said body with a chromium compound followed by a heat conversion of the chromium compound to an oxide, the improved method of hardening of same which comprises converting the chromium compound to an oxide at a temperature of at least about 1,300*F but below the vitrification temperture of said body.
 13. The method of claim 12 wherein there are at least two impregnation and conversion steps and all of the compound conversions steps are carried out at a temperature of at least 1, 300*F.
 14. The method of claim 12 wherein there are at least two impregnation and curing steps and includes one or more compound conversion steps at a temperature of at least 1,300*F and one or more compound conversion steps at a temperature of at least 600*F but less than 1,300*F.
 15. The method of claim 12 wherein the ceramic body is aluminum oxide.
 16. The method of claim 12 wherein the chromium compound is chromic acid.
 17. The method of claim 14 wherein the initial compound conversion step is carried out at at least 1,300*F.
 18. The method of claim 14 wherein the initial chromium compound conversion step is carried out at a temperature less than 1, 300*F.
 19. The method of claim 18 wherein the first five chromium compound conversion steps are carried out at tEmperatures less than 1,300*F.
 20. The method of claim 18 wherein the first ten chromium compound conversion steps are carried out at a temperature less than 1,300*F.
 21. The method of claim 17 where the chromium compound conversion steps are carried out alternately at temperatures below and above 1,300*F.
 22. The method of claim 18 where the chromium compound conversion steps are carried out alternately at temperatures below and above 1,300*F. 